1. Field of the Invention
The present invention relates to a brake system, and more particularly, to a method of controlling a brake force in a brake system including a front wheel system and a rear wheel system.
2. Description of the Related Art
An example of an electrically operated brake used for a vehicle is disclosed in Japanese Unexamined Patent Publication No. 3-41233 (corresponding to U. S. Pat. No. 5,107,967). This electrically operated brake operates as described below. In order to generate the required brake force, torque of an electric motor is transmitted to a brake friction pad via a worm mechanism for converting a rotary motion into a linear motion. As a result, the brake force is applied to the vehicle. At this time, the brake force is controlled in such a manner that a rotary angle of the electric motor is detected by an encoder and the position of the brake friction pad is controlled according to the rotary angle.
In another example of an electrically operated brake used for a vehicle, instead of the rotary angle of the electric motor, the pushing force of the brake friction pad is detected by a sensor. The brake force is then controlled by the detected pushing force.
However, the above braking devices have the following problems. The encoder for detecting a rotary angle of the motor and the brake friction pad pushing force sensor for detecting a pushing force of the brake friction pad are arranged in each braking device of the front and the rear wheels. In other words, the encoder and the brake friction pad pushing force sensor must be arranged in each of the four braking devices of a vehicle. This allows the brake force of each braking device to be controlled by an electronic control unit according to an output signal sent from each encoder and sensor. Since each sensor must be arranged in a brake caliper, the sensor has to be able to resist rough conditions such as high temperatures and intense vibrations. As a result, the cost of the sensor is raised. It is difficult to reduce the overall cost of the braking device.